Monitoring a condition of a subject, such as a subject at rest on a mattress, can include monitoring vital signs, such as heart and respiration rates. Some monitoring systems can include expensive and cumbersome equipment, such as an electrocardiogram (EKG), a ballistocardiograph (BCG), a piezoelectric film, or an array of sensors. EKGs, for example, typically necessitate attaching electrodes in substantially direct contact with a subject, while BCGs rely on large, heavy, unaesthetic force-measuring platforms.
In some implementations, monitoring a condition of a subject can include monitoring the presence or absence of a subject, for example, the presence or absence of a subject on a mattress. However, in addition to being expensive and cumbersome, monitoring systems can be unable to accurately predict when a subject is about to change condition, for example, when a presence condition is about to change from present to absent base on the subject exiting the mattress.